Method for calibration of feed rate of a metering device and a metering device

ABSTRACT

A method and system for calibrating the feed rate of a metering device for airflow-borne feeding of granular material in an agricultural implement. The method of calibrating the feed rate of the metering device comprises a first volumetric feeder with a first metering rotor arranged to feed granular material to an airflow channel.

TECHNICAL FIELD

The present document relates to a method for calibration of feed rate ofa metering device for airflow-borne feeding of granular material in anagricultural implement. The method can be used in agriculturalimplements using airflow-borne feeding, such as seed drills.

The document also relates to a metering device for airflow-borne feedingof granular material in an agricultural implement, which metering devicecan be calibrated according to the abovementioned method.

BACKGROUND

It is known in agricultural implements such as seed drills to use agenerated airflow to transport granular or powdered material, such asseed, fertilizer or pesticides, from a container via a distributor andonward via channels to a plurality of feeder tools, such as furrowopeners, etc. A feeder with a rotor can be used to feed material fromthe container to the airflow. By using a feeder, the correct amount ofmaterial being fed to the airflow can be ensured.

Such volumetric feeders have previously been used together with amechanical coupling to a blade impeller, which engages with the soil,wherein the speed of the feeder is controlled mechanically in relationto the ground.

In recent years, electrically or hydraulically driven feeders have beenapplied to a greater extent, providing greater freedom to control thefeeder in relation to the travel speed.

Another trend is to increase the precision of the drilling, i.e. tocontrol the amount of seed to be fed per unit area more precisely, whichin turn makes it possible to optimize yield and growth.

Consequently, it is desirable to be able to calibrate the feeder, inorder to ensure that the correct amount of material is fed per unitarea. For example, this is the case when drilling, as it is usuallydesirable to ensure a certain amount of seed per unit area of e.g. afield. The desired amount of seed per unit area can depend on aplurality of parameters, such as the type of crops, the size of thegranules, the soil, etc.

One way of calibrating a feeder is to use one or more sensors to countthe number of granules passing one or more places in the airflowchannels and then, based upon these measured values, to adjust the feedrate of the feeder so that the desired amount to be fed is reached. Anexample of calibrating a feeder of an agricultural implement withairflow feeding of seed can be found in US 2014/0076217.

It can be advantageous in a number of situations to also feed one ormore additional products from the agricultural implement duringdrilling, besides the crop to be sown, so called mixed drilling. Forexample, a small amount of fertilizer can preferably be fed togetherwith the seeds. In this way, the crop gets access to some extranutrition, promoting its establishment. There may also be a reason forsowing two or more different types of crops simultaneously, such as whenone crop acts as a support plant for another crop, or when it is simplydesirable to sow different crops in the same field. Consequently, duringmixed drilling there is a container with the crop to be sown as well asone or more additional containers containing, for example, fertilizer orsome other type of additional crop. The contents from the containers arefed into a channel and transported onward using an airflow to a numberof feeder tools, such as furrow openers, in order then to be distributedacross the field.

One difficulty with calibration for mixed drilling is that the count ofgranules does not provide accurate values, since an unknown number ofparticles are added to the airflow. With regards to fertilizer, theparticles also vary greatly in size, usually from the size of dustparticles up to the size of peas. The granule mixture in the airflowmeans that the determination of the amount cannot be carried out bycounting, since the sensors for this cannot distinguish what aregranules to be counted and what are not.

Therefore, it is desirable to provide an improved calibration method andan improved device in this respect.

SUMMARY

One object is to provide an improved method for calibration of feed rateof a metering device for airflow-borne feeding of granular material inan agricultural implement, and thus an improved metering device forairflow-borne feeding of granular material in an agricultural implement.

The invention is defined by the attached independent patent claims.Embodiments are set forth in the dependent patent claims, in thedescription that follows and in the drawings.

According to a first aspect, a method for calibration of feed rate of ametering device for airflow-borne feeding of granular material in anagricultural implement is provided, wherein the metering devicecomprises a first volumetric feeder with a first metering rotor arrangedto feed a first granular material to an airflow channel, the methodcomprising:

to drive the agricultural implement during a first time period,

to drive only the first metering rotor at a first rotational speed forfeeding a first granular material during the first time period,

by means of a granule-counting device downstream of the first and secondfeeder, to count a number of fed granules in the airflow channel of thefirst granular material,

based on the number of granules and the first rotational speed, tocalculate a first feed rate of the first feeder,

to drive the agricultural implement during a second time period,

during the second time period, to drive the metering rotor of the firstfeeder so that a first predetermined granular feed rate is provided,

during the second time period, to feed a second granular or powderedmaterial by means of a second feeder to the airflow channel so that boththe first and the second material are fed into the airflow channel.

By driving the agricultural implement during a first period and drivingonly the first metering rotor during that period, while there is nofeeding from the second container to the airflow channel taking place,the first feeder can be calibrated separately. During this time period,there is only the first granular material in the airflow, ensuring thatthe counting of granules by the granule-counting device is accurate.There is no interference from any other material in the metering device.As a result of feedback from the granule-counting device concerning thenumber of fed granules in the airflow channel of the first granularmaterial and the fact that the first rotational speed of the meteringrotor is known, a calculation of a first feed rate of the first feedercan be carried out.

The granule feed rate is thus the number of fed granules of a granularmaterial, e.g. granules/m².

After calibration during the first time period, the number of granulesfor a certain rotational speed is thus known, alternatively, the numberof granules per step or other angular unit of the metering rotor.Additional known parameters in the calculation are the speed of theagricultural implement and the width over which the agriculturalimplement is feeding out.

Consequently, the rotational speed can then be set during the secondtime period in order to reach the desired feed rate from the firstfeeder.

The rotational speed of a volumetric feeder can be described as thenumber of pulses or steps the metering rotor should turn per distancetravelled.

The predetermined granule feed rate can be pre-programmed or entered bythe user. The desired value will depend on e.g. the type of crops, thedesired sowing density, soil etc.

The second material can be added to the airflow channel downstream ofthe feeding from the first feeder but upstream of the granule-countingdevice, viewed in the direction of the air flow. In conventionalcalibration, a count of the number of granules is misleading as twomaterials are mixed in the airflow and the count is carried out afterthe addition of two materials into the airflow channel. In the methodabove, however, a correct calibration can thus be carried out despitethe fact that a second material is added to the airflow channel afterthe addition of the first granular material, but before thegranule-counting device, viewed in the direction of the airflow.

Material from the airflow channel can be fed via a distributor to aplurality of feeder tools of the agricultural implement. The granulecount can be carried out downstream of the distributor viewed in thedirection of the airflow. For example, sensors can be located on some orall of the airflow channels running between the distributor head of thedistributor and the feeder tools. This results in obtaining a value asaccurate as possible for the number of granules passing, since valuesfrom a plurality of sensors can be used and e.g. an average or medianvalue of the number of granules can be calculated. An incorrect value,for example if one of the sensors stops working, does not have as muchimpact as if only one sensor were being used.

The method can further comprise receiving input from a user with respectto a desired change of the granule feed rate of ±10%, and adjusting therotational speed of the metering rotor so that a change of thepredetermined granule feed rate of ±10% is provided. During operation, auser can thus adjust a pre-programmed or previously entered value for adesired feed rate of a granular material which can be advantageous if,during drilling, the user discovers that an increase or reduction wouldbe appropriate under the existing circumstances.

Furthermore, the method can comprise for the second volumetric feeder tocarry out the steps:

to drive the agricultural implement during a third time period which isseparate from the first and second time periods and which falls beforethe second time period,

to drive the metering rotor of the second feeder during the third timeperiod at a second rotational speed for feeding of a granular material,

by means of the granule-counting device, to count a number of fedgranules in the airflow channel of the second granular material,

to calculate, based on the number of granules per unit time and therotational speed of the second metering rotor, a feed rate of the secondfeeder, and

during the second time period, to drive the metering rotor of the secondfeeder so that a second predetermined granule feed rate is provided.

In the event of the second container containing granular material, e.g.for simultaneous drilling of two different crops, the second containercan thus be calibrated separately during a third time period before thefirst and second material are mixed in the airflow channel.

During the third time period, the second feeder can be driven while thefirst feeder is not driven, so that said number of fed granules onlycorresponds to the number of granules fed by the second feeder.

Consequently, separately measured values for the first and secondfeeders are obtained.

Alternatively, during the third time period, the first feeder and secondfeeder can both be driven, so that said number of fed granulescorresponds to a sum of the number of granules fed from the first feederand the number of granules fed from the second feeder.Consequently, first a value corresponding to the feed rate of the firstfeeder is obtained, and then a value corresponding to the sum of thefeed rates of the first and second feeders. Based on the sum value, thefeed rate of the second feeder can be deduced.

Corresponding principles can also be applied to arrangements with threeor more feeders.

In the event of the metering device further comprising a thirdvolumetric feeder with a metering rotor arranged to feed a thirdgranular material to the airflow channel, the method can furthercomprise for the third volumetric feeder to carry out the steps:

to drive the agricultural implement during a fourth time period which isseparate from the first, second and third time periods and which fallsbefore the second time period,

to drive the metering rotor of the third feeder during the fourth timeperiod at a third rotational speed for feeding of a third granularmaterial,

by means of the granule-counting device, to count a number of fedgranules in the airflow channel of the third granular material,

to calculate, based on the number of granules and the rotational speedof the third metering rotor, a feed rate of the third feeder,

during the second time period, to drive the metering rotor of the thirdfeeder so that a third predetermined granule feed rate is provided, and

during the second time period, to feed the third granular material tothe airflow channel so that both the first and the second material aswell as the third material are fed into the airflow channel.

A third container can be used, for example, when drilling two differentcrops plus fertilizing, or when drilling three different crops. Thethird container is then calibrated separately during a fourth timeperiod and thus a rotational speed for the metering rotor of the thirdfeeder can then be set in order to obtain the desired feed rate of thethird granular material.

Furthermore, additional containers feeding material to the airflowchannel can be envisaged, which containers in this case are calibratedas described for the third container above.

The length of the first time period can be determined based on a measureof variation with respect to said number of fed granules in the airflowchannel, preferably based on the variance during a certain period oftime being below a predetermined value. Furthermore, a relationshipbetween the travel speed and the rotational speed based on said variancecan be determined. In this way, the agricultural implement is drivenduring such a long time period that the value from the granule-countingdevice can be seen to be stable and thus appropriate to use for thecalibration calculation. In this way, it is possible to compensate forsuch variations that can occur as a result of vibrations from the travelof the agricultural implement, and/or from variations in the granules'ability to flow under the effect of gravity.

According to a second aspect, a metering device for airflow-bornefeeding of granular material in an agricultural implement is provided,comprising:

a first container for a first granular material,

a first volumetric feeder with a first metering rotor arranged to feedthe first material from the first container to an airflow channel,

a second container for a second granular or powdered material,

a second volumetric feeder with a second metering rotor arranged to feedthe second material from the second container to the airflow channel,

the second feeder being arranged to feed the second material to theairflow channel downstream of the first feeder viewed in a direction ofthe airflow in the channel, and

the airflow channel being arranged to lead the first and second materialto a plurality of feeder tools of the agricultural implement,

a granule-counting device for counting the number of granules beingtransported in the airflow channel, the granule-counting device beingarranged downstream of the first and second feeder, and

a control unit for controlling the first and second feeder, the controlunit being arranged:

during a first time period, to drive only the first metering rotor at afirst rotational speed,

during the first time period, to collect data from the granule-countingdevice representing the number of granules,

based on said number of fed granules and the first rotational speed ofthe metering rotor, to calculate a first feed rate of the first feeder,and

during a second time period, to drive the first and second feeder, thefirst feeder being driven to provide a first predetermined granule feedrate.

The metering device can further comprise a distributor for onwardtransport of material from the airflow channel to the feeder tools via aplurality of airflow channels.

The granule-counting device can be arranged downstream of thedistributor viewed in the direction of the airflow.

The metering device can further comprise a user interface for displayinginformation to a user and for receiving commands from the user. In thisway, information can be displayed to the user, for example concerningthe number of granules by the feeders, the number of counted granules inthe airflow, the present granule feed rate, etc. The user also has theopportunity to input instructions into the metering device, for exampleconcerning the desired granule feed rate, etc.

The control unit of the metering device can further be arranged:

during a third time period, which is separate from the first and secondtime period and which falls before the second time period, to drive themetering rotor of the second feeder at a second rotational speed,

during the third time period, to collect data from the granule-countingdevice concerning the number of granules of the second granularmaterial,

based on the number of fed granules and the second rotational speed ofthe metering rotor, to calculate a second feed rate of the secondfeeder, and

during the second time period, to drive the second feeder to provide asecond predetermined granule feed rate of the second granular material.

In this way, the feeding is calibrated from the second containerseparately from the calibration of the first container, e.g. when thetwo containers contain two different crops to be planted.

Furthermore, the metering device can also comprise a third container fora third granular material, and a third volumetric feeder with a meteringrotor arranged to feed the third granular material from the thirdcontainer to the airflow channel, and the control unit being furtherarranged:

during a fourth time period, which is separate from the first, secondand third time period and which falls before the second time period, todrive the metering rotor of the third feeder at a third rotationalspeed,

during the fourth time period, to collect data from the granule-countingdevice concerning the number of granules of the third granular material,

based on the number of fed granules and the third rotational speed ofthe metering rotor, to calculate a third feed rate of the third feeder,and

during the second time period, to drive the first, second and thirdfeeder, the third feeder being driven to provide, for the third feeder,a third predetermined granule feed rate of the third granular material.

This means that separate calibration of a third container containinggranular material can be carried out.

The granule-counting device can comprise one or more sensors forcounting granules in one or more places in the airflow channel and/or inthe outgoing airflow channels from the distributor to the feeder tools.

The sensors register the number of granules passing, and the values froma plurality of sensors can be used to ensure as accurate results aspossible.

According to a third aspect, an agricultural implement is provided,comprising a metering device as described above.

The agricultural implement can be a seed drill, a precision seed drillwith a so-called nursing function, a device for spreading fertilizer orpesticides, or a combination of these.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic representation of a metering device for feedinggranular material.

FIG. 2 shows an agricultural implement comprising a metering deviceaccording to FIG. 1.

FIGS. 3a-3d show various feeding scenarios which can be provided using asystem like the one of the agricultural implement in FIG. 1.

DETAILED DESCRIPTION

FIG. 1 shows a schematic view of a metering device for airflow-bornefeeding of granular material in an agricultural implement. The meteringdevice 1 comprises a first container 4 for a first granular material M1,a second container 6 for a second granular or powdered material M2. Thefirst container connects to a first feeder 5 and the second containercomprises a second feeder 7. Furthermore, the metering device 1comprises a fan 2, an airflow channel 3 and a distributor 8. Thedistributor comprises a distributor head and a plurality of airflowchannels leading to a plurality of feeder tools 9 a-9 d of theagricultural implement. The metering device 1 further comprises agranule-counting device with one or more sensors 10 a, 10 b and acontrol unit 11.

The first container 4 is connected to the airflow channel 3 via thefirst feeder 5. Correspondingly, the second container 6 is connected tothe airflow channel 3 via the second feeder 7. The fan 2 is connected toan upstream portion of the airflow channel and a downstream portion ofthe airflow channel connects to the distributor 8. The distributor 8comprises a distributor head with a plurality of outlets, each of whichis connected to feeder tools 9 a-9 d via a respective airflow channel,e.g. in the form of a pipe or tube.

The sensors 10 a, 10 b of the granule-counting device are in FIG. 1arranged in connection to/from the outgoing airflow channels of thedistributor head 8.

The control unit 11 is connected to the feeders 5, 7 and to the sensors10 a, 10 b of the granule-counting device.

Granular material M1 from the first container 4 is fed to the airflowchannel 3 via the first feeder 5. The feeder is preferably a volumetricfeeder, but can also be of a different type. Material in the container 4mainly falls under the effect of gravity via a material inlet to thefeeder 5. The feeder 5 is designed with a metering rotor, which is e.g.divided into a plurality of delimited compartments which are open alongthe circumference of the metering rotor, and where each compartmentholds a predetermined volume. When the metering rotor rotates, materialis taken from the material inlet through an inlet opening so thatupwardly open compartments are filled. When the metering rotor continuesto rotate, each compartment's opening turns toward the airflow channel3, resulting in the granules therein falling down into the channel 3 bygravity.

The rotational speed of the metering rotor can be controlled using thecontrol unit 11, bringing about an increased or reduced amount ofgranules being fed from the container 4 to the channel 3. For example,the feeder can be driven by a stepping motor or by a motor withcontrollable speed.

In the airflow channel 3, material is transported onward in the deviceusing a generated airflow F. The airflow F is provided in a conventionalway using one or more fans 2, which can be hydraulically or electricallydriven. The fan generates an airflow which transports the material fromthe feeder 5 outlet in the airflow channel 3 to the feeder tools 9 a-9 dvia the airflow channel 3, the distributor head and the distributor'sairflow channels.

From the second container 6, a granular or powdered material M2 can befed via a second feeder 7 to the airflow channel 3. The second container6 can, for example, contain fertilizer to be added to the crops to beplanted, or an additional crop as a complement to the granular materialbeing fed from the first container 4, e.g. so-called “companion crop”.The second feeder 7 can be of the same type as the first feeder 5 or ofanother type, depending on the type of material to be fed from thesecond container 6. The second container 6 can be located so that itsmaterial is fed downstream, in the direction of the airflow F, of thefeeding from the first feeder 5. However, it could also be located sothat the feeding takes place upstream of the feeding from the firstcontainer 4.

The metering device 1 in FIG. 1 also comprises a granule-countingdevice. The granule-counting device can comprise one or more sensors 10a, 10 b for counting granules. The sensors can be located in differentplaces in the metering device 1. Preferably, a plurality of sensors arearranged in all or some of the airflow channels leading out from thedistributor head. Alternatively, or as a complement, one or more sensorscan be arranged in the airflow channel 3 upstream of the distributor 8,viewed in the direction of the airflow.

The sensors used for counting granules passing in the airflow at acertain time point can, for example, be of the optical, magnetic orultrasonic type, but it is also possible to use other types of sensors.By registering objects passing its sensing area, it is possible toobtain information on the number of granules passing a certain positionper unit time.

When a plurality of sensors are used for counting, the number ofgranules passing per unit time can be calculated by compiling data fromall the sensors, and based on this, calculating a value, e.g. an averagevalue based on output data from all the sensors. In this way, anacceptable result of the count is ensured, even if a single sensor forsome reason gives an incorrect value.

The information from the sensors 10 a, 10 b is sent to the control unit11 for further processing. The control unit 11 is arranged to receivesignals from the sensors 10 a, 10 b, to carry out calculations and tosend output signals to other units, e.g. to one or more feeders 5, 7 inthe metering device 1. The control unit 11 can comprise a single controlunit or a plurality of interacting control units. It can also bearranged to communicate with other devices on the agriculturalimplement, such as a device for displaying information to a user and forreceiving commands from the user. It is also conceivable that thecontrol unit 11 is arranged to send and receive signals from units notarranged on the agricultural implement, such as a remote server forstoring data, or an information unit for monitoring the status of theagricultural implement, etc.

Calibration of the feeding of the first granular material M1 from thefirst container 4 is carried out by the control unit 11 driving only thefirst feeder 5 during a first time period in order to feed granules ofthe first material into the airflow channel 3. The second feeder 2 c ofthe second container 6 (and any other feeders associated with additionalcontainers, if applicable) is not driven. The agricultural implement isdriven at a first speed V1 and has a known width B over which granularmaterial is fed. For the first granular material, there is a firstpredetermined feed rate per unit area TA1 which it is desirable toreach. The predetermined feed rate per unit area depends on the kind ofcrop involved, granule size, soil, etc. The predetermined value can bepre-programmed or is entered by the user when the agricultural implementis in use.

When the agricultural implement is driven during the first time period,the granule-counting device counts, by using one or more sensors, thenumber of granules passing per unit time when driving the metering rotorof the first feeder at a first rotational speed R1. This information issent to the control unit with which calculations can be made based onthe values obtained. Since the rotational speed R1 and the number ofgranules per unit time in the airflow are known variables, the number ofgranules fed per rotation or per step of the first feeder 5 can bedetermined.

Since the speed V and the width B (of the part of the working width ofthe machine being fed by the system) of the agricultural implement arealso known variables, the control unit can thus, after calibration,drive the first metering rotor at a speed enabling the desired number offed granules per unit area to be reached.

The metering device can further comprise a third container (not shown)with granular or powdered material connected to the airflow channel 3via a third feeder. For example, sometimes it can be desirable to sowtwo or more crops simultaneously, or to have several containers in orderto accommodate more material on the agricultural implement. It is alsoconceivable to include additional containers in the metering device,which are connected to the airflow channel 3.

In the event of having several containers with material, each feeder canbe calibrated separately during a respective time period until itsdesired feeding amount per unit area for the actual material is reached.

Calibration as described above can thus be carried out for allcontainers with associated feeders for granular material used in themetering device. By calibrating each container separately during acertain time period, the granule-counting device is not interrupted byirrelevant particles. Instead, an accurate count of the actual granulesis achieved.

It will be appreciated that calibration can be carried out by runningone feeder at a time, wherein the measured value for each of the feedersis achieved.

Alternatively, the feeders can be activated sequentially, wherein eachactivation is followed by a measurement/count before the next feeder isactivated. Each measured value will thus correspond to the sum offeedings from the active feeders.

Information can be sent within the metering device 1, as well as to andfrom the same, wirelessly or wired depending on the existingcircumstances.

The length of the first time period can be a predetermined value, e.g.corresponding to a certain time. Alternatively, the length of the periodcan correspond to a certain distance and can also be dependent on thetravel speed during the first time period.

As an additional alternative, the length of the time period can bedynamic, for example dependent on a measurement of the variance of themeasured feed rate. The variance can then be measured in a rollingmanner during a predetermined time period, e.g. 10-30 seconds, until apredetermined time average of the variance measurement is reached. Forexample, any form of measurement of variance or standard deviation canbe used as a variance measurement.

If such a time average is not reached within a certain period of time,the procedure can be restarted, an error message provided, or thepredetermined time average adjusted upward, so that greater variation isallowed.

In FIG. 2, an agricultural implement 100 is shown which comprises a pairof containers 40, 60 and a pair of feed systems acting in parallel andcorresponding to the description above: a right-hand feed system and aleft-hand feed system.

In the example shown, both feed systems get material from bothcontainers 40, 60. It will be appreciated that each system can have itsown, separate container.

The feed system comprises a fan 20 arranged to provide an airflowaccording to the description above.

In the example shown, the fan feeds the airflow to a cavity inside aportion of the frame 30 of the agricultural implement.

Only the right-hand feed system is described below, and then withreference to FIGS. 3a-3d , but it will be appreciated that the left-handfeed system can be designed in an analogous way. It will also beappreciated that more than two feed systems can be provided, for examplethree, four or five feed systems acting in parallel.

In FIGS. 3a-3d , a first feed circuit is provided, through which a reardistributor 80 b is fed, and a second feed circuit, through which afront distributor 80 f is fed.

From the cavity, a first outlet 33 leads to a first channel that forms afirst feed circuit. Furthermore, a second outlet 34 from the cavityleads to a second channel 32, which forms a second feed circuit.

The outlets can be provided with respective controllable valves (in amanner known per se), so that the feeding from the feeder can be ledselectively to one or more alternative, or complementing, channels,making it possible to provide greater flexibility for feeding.

In the example shown, there are two containers 40, 60 (FIG. 2), andfeeders 50, 70, associated with a respective container, which feederscan both feed material selectively to both channels 31, 32.

Through this arrangement, it is therefore possible to selectivelyprovide feeding of two or more crops or materials to two or moredistributors.

In the system shown, both feeders, therefore, have a respective “switch”making it possible to control the feeding from a respective feeder 50,70 to one of two parallel channels 31, 32. In FIGS. 3a-3d , a closedoutlet is indicated by “X”.

In this way, it is possible to provide a number of different feedingscenarios.

According to a first scenario, shown in FIG. 3a , only the rear furrowopeners 90 b are used, which furrow openers are fed via the reardistributor 80 b.

In this scenario, material can be fed from the front container 40 andfrom the rear container 60. Both materials are then fed via the firstoutlets of the respective feeder to the same channel 31, while thesecond outlets of the respective feeder are closed. The valvecontrolling the supply flow 33 to the first channel 30 is open here, andthe valve controlling the supply flow 34 to the second channel 32 can beclosed here.

According to a second scenario, shown in FIG. 3b , only the front furrowopeners are used, which furrow openers are fed via the front distributor80 f. In this scenario, material can be fed from both containers via thesecond channel 32, wherein the valve controlling the supply flow 34 isopen, and the valve controlling the supply flow 33 to the first channel31 can be closed.

The first outlets of both feeders are closed here, and the secondoutlets of both feeders are open, so that material is fed to the secondchannel 32.

The scenarios shown in FIGS. 3a and 3b can be used for so-called “mixeddrilling”.

According to a third scenario, shown in FIG. 3c , both supply flows 33,34 can be open while the first outlet of the front feeder 50 is closedand the second outlet of the rear feeder 70 is closed. Consequently,material is fed from the first feeder 50 via the rear distributor 80 bto the rear furrow openers, and material from the second feeder 70 isfed via the front distributor 80 f to the front furrow openers.

According to a fourth scenario, shown in FIG. 3d , both supply flows 33,34 can be open while the second outlet of the front feeder 50 is closedand the first outlet of the rear feeder 70 is closed. Consequently,material is fed from the first feeder 50 via the front distributor 80 fto the front furrow openers, and material from the second feeder 70 isfed via the rear distributor 80 b to the rear furrow openers.

The scenarios shown in FIGS. 3c and 3d can be used for so-called “combidrilling”.

For example, the material provided from the front feeder can be a maincrop, and the material provided from the rear feeder can be a secondmaterial, e.g. fertilizer or a “companion crop”.

It will be appreciated that the left-hand, or additional, feed systemcan be designed and driven in the same way.

It will also be appreciated that each feed system can comprise more thantwo feeders, e.g. 3, 4 or 5 feeders, sequentially feeding material toone or more airflows.

Calibration of a respective feeder can be provided in accordance withthe description above, i.e. by carrying out a calibration run withgranule counting for each feeder while the other feeders are turned off.

Furthermore, it will be appreciated that for feeders feeding materialnot suitable for counting by the granule counter, such as e.g.fertilizer or pesticides, calibration can be carried out individually,in a known manner, through a so-called tensile test.

Furthermore, it will be appreciated that even though it is not possibleto count granules during operation with an acceptable accuracy, thegranule-counting sensors 10 a, 10 b can still be used during operationin progress.

For example, the granule counters can be used to provide an indicationof whether feeding is in progress or not: even though the feeders do notshow the correct number of granules, they can still show that there is aflow of material in a respective line, which can also be used as anindication that the feeding is working.

Furthermore, the granule counters can be utilized to assess whether thedistribution between the outgoing channels from the distributor 9, 80 iswithin acceptable limits, or whether a stop has occurred in any of theoutgoing lines.

By providing all channels with granule counters, such an indication canbe provided for all channels.

Depending on the type of material being fed, it is also possible totrack the distribution for a given combination of material over time,even though an exact value of the number of granules is not provided.

1. A method for calibration of feed rate of a metering device forairflow-borne feeding of granular material in an agricultural implement,the metering device comprising: a first volumetric feeder with a firstmetering rotor arranged to feed a first granular material to an airflowchannel, and a second volumetric feeder with a second metering rotorarranged to feed a second granular or powdered material to the airflowchannel, the method comprising: to drive the agricultural implementduring a first time period, to drive only the first metering rotor at afirst rotational speed for feeding a first granular material (M1) duringthe first time period, by means of a granule-counting device, to count anumber of fed granules in the airflow channel of the first granularmaterial, based on the number of granules and the first rotationalspeed, to calculate a first feed rate of the first feeder, to drive theagricultural implement during a second time period, to drive the firstmetering rotor during the second time period so that a firstpredetermined granular feed rate is provided, and to drive the secondmetering rotor during the second time period so that both the first andthe second material are fed into the airflow channel.
 2. The methodaccording to claim 1, wherein the second material (M1) is added to theairflow channel downstream of the feeding from the first feeder butupstream of the granule-counting device, viewed in the direction of theair flow.
 3. The method according to claim 1, wherein the secondmaterial is added to the airflow channel upstream of the feeding fromthe first feeder but upstream of the granule-counting device, viewed inthe direction of the air flow.
 4. The method according to claim 1,wherein material from the airflow channel is fed via a distributor to aplurality of feeder tools of the agricultural implement.
 5. The methodaccording to claim 4, wherein said number of fed granules per unit timeof the first granular material is counted downstream of the distributorviewed in the direction of the airflow.
 6. The method according to claim1, further comprising, during the second time period, to receive inputfrom a user with respect to a desired change of the granular feed rate,and to adjust the rotational speed of the metering rotor so that acorresponding change of the predetermined granule feed rate is provided.7. The method according to claim 1, wherein the method furthercomprises: for the second volumetric feeder to carry out the steps: todrive the agricultural implement during a third time period which isseparate from the first and second time periods and which falls beforethe second time period, to drive the metering rotor of the second feederduring the third time period at a second rotational speed for feeding ofa granular material, by means of the granule-counting device, to count anumber of fed granules in the airflow channel of the second granularmaterial, based on the number of granules per unit time and therotational speed of the second metering rotor, to calculate a feed rateof the second feeder, and during the second time period, to drive themetering rotor of the second feeder so that a second predeterminedgranule feed rate per unit area is provided.
 8. The method according toclaim 7, wherein, during the third time period, the second feeder isdriven while the first feeder is not driven, so that said number of fedgranules only corresponds to the number of granules fed by the secondfeeder.
 9. The method according to claim 7, wherein, during the thirdtime period, the first feeder and second feeder are both driven, so thatsaid number of fed granules corresponds to a sum of the number ofgranules fed from the first feeder and the number of granules fed fromthe second feeder.
 10. The method according to claim 1, wherein thelength of the first time period is determined based on a measure of thevariation of said number of fed granules in the airflow channel,preferably based on a variance or a standard deviation, during a certainperiod of time, being below a predetermined value.
 11. The methodaccording to claim 1, wherein, during the first time period, only thefirst metering rotor is driven, and wherein the granule-counting deviceis arranged downstream of the first and second feeder.
 12. A meteringdevice for airflow-borne feeding of granular material in an agriculturalimplement, comprising: a first container for a first granular material,a first volumetric feeder with a first metering rotor arranged to feedthe first material from the first container to an airflow channel, asecond container for a second granular or powdered material, a secondvolumetric feeder with a second metering rotor arranged to feed thesecond material from the second container to the airflow channel, thesecond feeder being arranged to feed the second material to the airflowchannel, and the airflow channel being arranged to lead the first andsecond material to a plurality of feeder tools of the agriculturalimplement, a granule-counting device for counting the number of granulesbeing transported in the airflow channel, the granule-counting devicebeing arranged downstream of the first and second feeder, and a controlunit for controlling the first and second feeder, the control unit beingarranged: during a first time period, to drive only the first meteringrotor at a first rotational speed, during the first time period, tocollect data from the granule-counting device representing the number ofgranules, based on said number of fed granules per unit time and thefirst rotational speed of the metering rotor, to calculate a first feedrate of the first feeder, and during a second time period, to drive thefirst and second feeder, the first feeder being driven to provide afirst predetermined granule feed rate.
 13. The metering device accordingto claim 12, further comprising a distributor for onward transport ofmaterial from the airflow channel to the feeder tools via a plurality ofairflow channels.
 14. The metering device according to claim 13, whereinthe granule-counting device is arranged downstream of the distributorviewed in the direction of the airflow.
 15. The metering deviceaccording to claim 12, further comprising a user interface fordisplaying information to a user and for receiving commands from theuser.
 16. The metering device according to claim 12, wherein the controlunit is further arranged: during a third time period, which is separatefrom the first and second time period and which falls before the secondtime period, to drive the metering rotor of the second feeder at asecond rotational speed, during the third time period, to collect datafrom the granule-counting device representing the number of granules perunit time of the second material, based on the number of fed granulesper unit time and the second rotational speed of the metering rotor, tocalculate a second feed rate of the second feeder, and during the secondtime period, to drive the second feeder to provide a secondpredetermined granule feed rate per unit area of the second material.17. The metering device according to claim 12, wherein thegranule-counting device comprises one or more sensors for countinggranules in one or more places in the airflow channel and/or in theoutgoing airflow channels from the distributor to the feeder tools. 18.An agricultural implement comprising at least one metering deviceaccording to claim 12.